With increasing development of electronic products, the manufacturers keep improving the power modules of the power supply systems of the electronic products. For example, hot-swappable power modules have been introduced to the market. During the operation of a power module, the heat generated from the power module should be exhausted to the ambient air by an active heat-dissipating mechanism (e.g. a fan) in order to maintain the performance of the power module.
FIG. 1A is a schematic circuit block diagram illustrating a conventional power module. As shown in FIG. 1A, the conventional power module 1 comprises a power conversion circuit 10, a controlling unit 11, a first fan 12 and a second fan 13. The power conversion circuit 10 is configured to convert an input voltage Vin into a DC voltage Vo. The first fan 12 and the second fan 13 are connected with the output terminal of the power conversion circuit 10 in parallel. The controlling unit 11 is electrically connected with the first fan 12 and the second fan 13. After the rotating speed signals Vrs1 and Vrs2 outputted from the first fan 12 and the second fan 13 are received, the controlling unit 11 issues corresponding control signals PWM to the first fan 12 and the second fan 13.
FIG. 1B is a schematic timing waveform diagram illustrating associated signals processed in the power module of FIG. 1A. As shown in FIG. 1B, the control signal PWM is a rectangular wave. In response to a high logic level of the control signal PWM, an output current is transmitted from the output terminal of the power conversion circuit 10 to the first fan 12 and the second fan 13, thereby driving rotations of the first fan 12 and the second fan 13. Whereas, in response to a low logic level of the control signal PWM, no current is inputted into the first fan 12 and the second fan 13. Since the first fan 12 and the second fan 13 are not driven, the first fan 12 and the second fan 13 are continuously rotated because of the inertial motion. Under this circumstance, the rotating speeds of the first fan 12 and the second fan 13 are slowly reduced. Since the rotating speeds of the first fan 12 and the second fan 13 are adjustable according to the control signal PWM, the first fan 12 and the second 13 are not necessarily operated at the maximum rotating speeds. In this situation, a power-saving purpose is achieved.
Please refer to FIG. 1B again. In response to the low logic level of the control signal PWM, the first fan 12 and the second fan 13 are not driven. Meanwhile, the DC voltage Vo is equal to the preset voltage (e.g. 12V). Whereas, in response to the high logic level of the control signal PWM, the first fan 12 and the second fan 13 are driven. Since the energy for rotating the first fan 12 and the second fan 13 is provided by the output terminal of the power conversion circuit 10, the magnitude of the DC voltage Vo decreases. That is, the DC voltage Vo is pulled down to be lower than 12V. Due to the surge effect of the DC voltage Vo, the output performance is impaired.
Please refer to FIG. 1A again. In a case that the control signal PWM fails to be transmitted to the first fan 12 and the second fan 13 (e.g. in a floating state), the first fan 12 and the second fan 13 are disabled. Consequently, the overall temperature of the power module 1 is increased. If the power module 1 is overheated, the power module 1 is possibly damaged.
For avoiding the surge effect of the DC voltage, another power module is disclosed. FIG. 2A is a schematic circuit block diagram illustrating another conventional power module. For avoiding the surge effect of the DC voltage Vo during operations of the first fan 12 and the second fan 13, a capacitor C is connected with the output terminal of the power conversion circuit 10 in parallel. The capacitor C has a large capacitance value for filtering the DC voltage Vo. In such way, regardless of whether, the first fan 12 and the second 13 are rotated or not, a stable DC voltage is outputted. Although the power module 21 of FIG. 2A is effective to avoid the surge effect of the DC voltage encountered from the power module 1 of FIG. 1A, there are still some drawbacks.
FIG. 2B is a schematic circuit block diagram illustrating a power supply system with the power module of FIG. 2A. The power supply system 2 is connected with a load 4. The power supply system 2 comprises plural power modules 21, plural connectors 22 and a power distribution circuit 23. For clarification, only two power modules 21 and two connectors 22 are shown. The power modules 21 are connected with the power distribution circuit 23 through corresponding connectors 22. These power modules 21 are hot-swappable. That is, during the operation of the power supply system 2, the power modules 21 may be directly removed from the connectors 22 or connected with the connectors 22. Since the capacitor C of the power module 21 has a large capacitance value, if the power module 21 has been disabled for a time period, no charge is stored in the capacitor C. If the power module 21 is connected to an enabling power supply system 2, the capacitor C with no charge is transiently in a short-circuited state. Meanwhile, since a large current is abruptly inputted into the connector 22 and the capacitor C, the possibility of burning out the connector 22 and the capacitor C will be increased.